The catch … a minke whale on the slipway of the factory vessel Nisshin Maru on February 15. Photo: AFP

''Concussion grenades are being deployed against the Bob Barker, and near the tanker. They have made another run, ramming the Sam Simon in the port quarter. It's a very intense situation.''

Earlier, the 12,500- tonne Japanese Maritime Self-Defence Force icebreaker Shirase approached the scene in Mackenzie Bay, near the coast of the Australian Antarctic Territory far south-west of Perth.

Advertisement

A helicopter from the Shirase flew over the Sun Laurel, and kept course with it, Mr Watson said.

The Environment Minister, Tony Burke, said Japan needed to confirm the Shirase and the tanker were not linked.

''Japan has told the government that the Shirase is not involved in supporting their so-called scientific whaling fleet,'' Mr Burke said

''If there is no link or support to the Japanese whaling fleet, has there been a link, support or transfer of Japanese personnel to the South Korean tanker?'' he said. ''The tanker is the life blood for the rest of this disgusting operation.''

The Shirase was first detected on Sea Shepherd's radar by its ship's automatic identification signal, and at last report, Mr Watson said it was visible on the horizon about 12 nautical miles away.

Asked whether the appearance of the Shirase meant it would be used in the conflict, representing an escalation of the situation, Japan's consul-general in Melbourne, Hidenobu Sobashima, said: ''There are no such facts as alleged.

''We are not in a position to make a statement on the movement of the ships,'' he said.

The icebreaker was scheduled to be in the region conducting Antarctic marine scientific work off nearby Cape Darnley, an informed Australian source said.

The blockade by Sea Shepherd stopped the Nisshin Maru from reaching the Sun Laurel last Wednesday.

Instead the whalers' mother ship was involved in a series of damaging collisions with the three Sea Shepherd vessels, and with the Sun Laurel.

The collisions raised fears of injury, or a fuel spill in pristine Antarctic waters far from aid.

After they parted, the Sun Laurel headed out of the sea ice zone, while the Nisshin Maru stayed in the region. Japan denied that its whaling program had been suspended.